Figure 5.

Time course of telomere shortening after disruption of the rad1⁺ gene and of restoration of wild-type telomeres after reintroduction of wild-type rad1⁺. Wild-type strain h⁺ ura4-D18 leu1-32 his3 was transformed with pr1u4 and DNA was isolated at various times thereafter. D, point where the rad1⁺ gene was disrupted; R, point where the rad1⁺ gene was reintroduced. Brackets above lanes indicate where the rad1⁺ gene was expressed from a multicopy plasmid (pIRT2R1). Southern blot as described in the legend to Figure 1. Lane 1, DNA was isolated before disruption (0 h); lane 2, 30 generations postdisruption (transformant colony expanded to 5 × 10⁸ cells); lane 3, 60 generations; lane 4, 100 generations postdisruption. The disruptant strain was then transformed with plasmid pIRT2R1 containing the wild-type rad1⁺ gene. Lane 5, 30 generations after reintroduction of rad1⁺; lane 6, 50 generations; lane 7, 100 generations.